1. Field of the Invention
The invention relates to a method for blood pressure measurement, in which method a variable compressive acting pressure is applied to a measuring point, such as a person""s extremity or the like, at a compression point by a pressure generator, and at the same time the effect of the variable pressure on the artery is measured at a second point, the second point being located farther away from the heart, i.e. closer to the end point of peripheral circulation than the compression point to which the pressure is applied, and in which method diastolic pressure and/or systolic pressure is determined to determine the measurement result of an actual blood pressure measurement.
A second embodiment of the invention relates to a method for blood pressure measurement, in which method a variable compressive acting pressure is applied to a measuring point, such as a person""s extremity or the like, at a compression point by a pressure generator, and in which method diastolic pressure and/or systolic pressure is determined oscillometrically to determine the measurement result of an actual blood pressure measurement by measuring a pressure oscillation signal which is measurable from the pressure generator.
The invention also relates to an arrangement for blood pressure measurement, comprising a pressure generator for applying an acting pressure to a measuring point, such as a person""s extremity or the like, the arrangement comprising a measuring element for measuring the acting pressure, the arrangement further comprising an interpreting unit for determining systolic pressure and/or diastolic pressure, the arrangement comprising a sensor for simultaneous measurement of the effect of the variable pressure on an artery at a second point, said second point being farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied.
The second embodiment of the invention relates to an arrangement for blood pressure measurement, comprising a pressure generator for applying an acting pressure to a measuring point, such as a person""s extremity or the like, the arrangement comprising a measuring element for measuring the acting pressure and its effect by measuring a pressure oscillation signal of the pressure generator, the arrangement further comprising an interpreting unit for determining systolic pressure and/or diastolic pressure oscillometrically from the pressure oscillation signal.
2. Brief Description of the Related Art
The heart pumps and causes blood to flow in the blood vessels, arteries and veins. The pumping produces pressure in the blood, i.e. blood pressure. Blood pressure is particularly affected by heartbeat and the resistance provided by peripheral circulation. Psychic factors, medication, smoking and other factors, such as a person""s state, i.e. whether a person is asleep or awake, are also important.
The terms systolic pressure, diastolic pressure and venous pressure, are used when discussing blood pressure.
Technically, from the point of view of measurement, systolic pressure refers to the pressure at which an artery becomes blocked, i.e. heartbeat stops. Physiologically, systolic pressure refers to the maximum pressure generated by a pumping cycle of the heart.
Technically, from the point of view of measurement, diastolic pressure refers to the pressure at which heartbeat is resumed when the pressure pressing the artery is reduced. Physiologically, diastolic pressure refers to the minimum venous pressure value between two pumping cycles of the heart.
Venous pressure refers to the average pressure in a vein. At a certain stage of venous pressure measurement, a systolic and diastolic point can also be detected.
Blood pressure measurement is divided into two main categories: invasive, i.e. measurement from inside the body, and non-invasive, i.e. measurement from the outside of the body. The drawback in the invasive method is naturally that the measurement is made from inside a person""s body by the use of e.g. a catheter placed in an artery. The invasive method and the equipment solutions involved are unpleasant for a person, and the measurements involve much work and are cumbersome, since they require operating theatre conditions. A special drawback is the risk of infection and bleeding of the artery.
Currently two methods are known for non-invasive blood pressure measurement, i.e. measurement from outside of the body. These include the auscultatory measurement and the oscillometric measurement. The auscultatory method utilizes a stethoscope and an occluding cuff provided with a mercury manometer and a pressure pump, the cuff encircling a person""s extremity, such as the arm. The auscultatory method is based on auscultation of sounds known as the Korotkoff sounds by the stethoscope. The Korotkoff sounds are created by blood flowing in a partially occluded artery. In the auscultatory method the pressure of the occluding cuff, i.e. the acting pressure, is first raised above the estimated systolic pressure, whereby blood flow in the extremity being measured, such as the arm, is occluded. The pressure of the occluding cuff is then allowed to decline gradually, while the stethoscope is placed over the artery for auscultation on the distal side with respect to the occluding cuff. Once the pressure has been lowered sufficiently, snapping Korotkoff sounds can be detected by the stethoscope, and the current pressure is interpreted as the systolic pressure. Once the pressure of the occluding cuff is allowed to decline further, Korotkoff sounds are no longer heard, which means that the current pressure is the diastolic pressure at which the occluding cuff no longer occludes the artery. The drawback of the auscultatory method is its inaccuracy and that it requires an intent and experienced user.
Publication DE-2605528 teaches an application of the auscultatory method which additionally utilizes an optic pulse sensor disposed on the finger for following the variations in the pressure pulse. If the pressure pulse measured by the optic pulse sensor is observed to vary, this indicates a change in blood pressure from the previous measurement, and requires a new measurement. However, said procedure does not allow, recognize or suggest improvement of accuracy and reliability, only that said information indicates the need for a repeat measurement.
Furthermore, a manual method based on palpation is known, in which pressure is produced by an occluding cuff in the arm, and a finger is used to palpate the pressure pulse of the radial artery, i.e. heartbeat. However, said method is inaccurate and unreliable.
Another widely used non-invasive method is the oscillometric measurement, in which an occluding cuff and the same principle are used, i.e. the acting pressure is first raised high, i.e. over the estimated systolic pressure, and then slowly declined, during which a pressure sensor comprised by the cuff is used to follow or observe the pressure oscillation signal of the cuff. Thus the essential difference as compared with the auscultatory method is that in the oscillometric method an electronic monitoring unit comprised by the device is used to follow the pressure oscillation measured by the pressure sensor inside the cuff instead of auscultation of an artery. As cuff pressure falls, the amplitude of the pressure oscillation in the cuff, i.e. the AC signal of the cuff pressure, increases to a certain pressure as the pressure is lowered, whereupon the oscillation decreases. When the pressure falls, oscillation, i.e. an AC-form pressure oscillation signal, or amplitude variation, is detectable in the cuff pressure. The amplitude of the pressure oscillation signal oscillation measured by the pressure sensor from the cuff reaches its maximum at a pressure known as mean arterial pressure. Systolic pressure can be measured relatively well by the oscillometric method, but diastolic pressure has to be calculated indirectly since the pressure oscillation signal oscillation measured by the cuff pressure sensor is still present at diastolic pressure, and hence indirect determination is used, in which the value of the diastolic pressure is the mean arterial pressure minus half of the difference between systolic and mean arterial pressure. A weakness of the oscillometric method is its inaccuracy and the resulting unreliability. Oscillometric devices and methods are technically simple, but this in turn results in the inability to monitor and observe the measurement and its reliability. The accuracy and reliability of oscillometric measurement have been improved by different signal processing methods by identifying different characteristics of the AC signal of the pressure pulse during measurement in association with determination of systolic and diastolic pressure. Publication U.S. Pat. No. 4,117,835, for example, discloses a method of monitoring the change in the AC signal derivative. However, in clinical measurements said methods have not been found to affect the accuracy.
A tonometric method, originally designed for ocular pressure measurement, has also been applied to blood pressure measurement. In the methods according to publication U.S. Pat. No. 5,033,471, the radial artery extending near a radius of the wrist is pressed. Since the surface resting against the sensor is even, intravenous pressure can be read at the middle sensor element. The method thus involves a direct non-invasive measurement. In principle the measurement is ideal and practical, but the skin causes a problem since it does not provide an ideal membrane between the sensor and the blood vessel. This is why calibration is required in tonometric methods, as described in e.g. publication U.S. Pat. No. 5279303.
Known methods and measurement arrangements provide no reliable way to estimate measurement quality, or reliability.
A common problem in non-invasive blood pressure meters is inaccuracy. Part of the inaccuracy is the result of physiological factors, such as normal blood pressure variation and change, even during measurement. Additional inaccuracy is caused by the inaccuracy of the measurement method and the meter. Measurement error can be as high as 10 mm Hg, but known meters do not allow the user to estimate the accuracy of the systolic and/or diastolic pressure reading. Often the user imagines that the accuracy of the last meter number, i.e. 1 mm Hg, is the accuracy of the meter, although in reality the inaccuracy may be as much as xc2x15 or xc2x110 mm Hg.
It is an object of the present invention to provide a new kind of method and arrangement for blood pressure measurement, avoiding the problems of known solutions.
The object is achieved by a method according to a first embodiment of the invention, characterized in that in addition to the actual blood pressure measurement, the method comprises an estimation cycle for the actual measurement, during which the magnitude of the pressure pulse is measured by a sensor measuring a pressure pulse signal, and that in the estimation one or more statistical parameters are calculated from the pressure pulse measurement data to represent the magnitude of pressure pulse variation for forecasting and/or depicting the quality of the actual blood pressure measurement.
The object is also achieved by a method according to a second embodiment of the invention, characterized in that in addition to the actual blood pressure measurement, the method comprises an estimation cycle for the actual measurement, during which the magnitude of the pressure oscillation signal is measured by a sensor measuring the pressure oscillation signal, and that in the estimation one or more statistical parameters are calculated from the pressure oscillation signal measurement data to represent the magnitude of pressure oscillation signal variation for forecasting and/or depicting the quality of the actual blood pressure measurement.
In the first embodiment, the measurement arrangement of the invention is characterized in that it comprises an estimation means for estimating the quality of an actual blood pressure measurement, and that the estimation means is in connection with the sensor measuring the pressure pulse at the measuring point and feeding the measurement data to the estimation means, the sensor being either the same sensor that is used in the actual blood pressure measurement for measuring the effect of the acting pressure, or a second, different sensor, and that the estimation means comprises a calculation means, adapted to calculate from the measurement data measured by the pressure pulse sensor one or more statistical parameters representing the magnitude of pressure pulse variation for forecasting and/or depicting the quality of the actual blood pressure measurement.
In the second embodiment, the measurement arrangement of the invention is characterized in that it comprises an estimation means for estimating the quality of an actual blood pressure measurement, and that the estimation means is in connection with the measuring element or with another sensor measuring the pressure oscillation signal and feeding the measurement data to the estimation means, and that the estimation means comprises a calculation means, adapted to calculate from the measurement data of the measured pressure oscillation signal one or more statistical parameters representing the magnitude of pressure oscillation signal variation for forecasting and/or depicting the quality of the actual blood pressure measurement.
The method and measurement arrangement of the invention are based on the idea that the actual blood pressure measurement is estimated on the basis of a pressure pulse measurement or a pressure oscillation signal measurement made before and/or after the actual blood pressure measurement.
The solution of the invention provides several advantages. By means of the invention, the user or nursing staff receive valuable additional information on the accuracy and representativeness of the result of the blood pressure measurement. Measurements of diastolic and systolic pressure are discrete measurements, and the invention allows the practicability of such a discrete measurement to be improved. The invention allows the rejection of measurement results the estimation result of which, calculated in the manner according to the invention, is too weak, and, on the other hand, allows the acceptance of measurement results with sufficiently good estimation results.
More reliable measurement results allow the right conclusions to be drawn from a person""s real blood pressure values. Technically, the measurement arrangement of the invention can be implemented within a small space, if desired, e.g. as a wristband. Some parts of the measurement arrangement of the invention, such as the pressure pulse meter or the interpreting unit, can be applied to actual blood pressure measurements, if desired, in addition to the estimation of measurement quality.
The present invention is particularly well suitable for a novel palpation method which utilizes a sensor measuring arterial pressure pulse, but the invention can also be applied to oscillometric applications, in which measurements are carried out by a pressure cuff.